Natural Hybridization of Two Invasive Carps: Perspectives from Genomics, Transcriptomics and Cross Experiments

A unique situation occurs throughout the Mississippi River Basin (MRB) where two introduced sympatric carps rampantly hybridize but remain genetically isolated within their native range. Bighead Carp and Silver Carp were introduced to the US in 1970’s and hybrids of the carps were sampled in early 1980’s. The carps have attained a high degree of genetic admixture between parental species during the past decade. In this study, the analysis of high-throughput RAD-Sequencing data revealed low genetic diversity with inbreeding occurring in invasive bigheaded carps. Comparative transcriptomics using RNA-Seq showed that the two bigheaded carps shared the majority of total transcripts with most functional genes and metabolic pathways found in parental species also presented in the hybrids. Gamete incompatibility of the two carps and embryonic less fitness of hybrids were not observed in the cross experiments. Our results suggest the low genetic diversity resulted from the inbreeding of a possible small populations of founders and the genomic comparability between the two species are two major causes, although ecological factors are also important, that are contributed to the success of natural hybridization of bigheaded carps in the MRB.